Authentication value for fluid ejection device

ABSTRACT

A fluid ejection device includes a plurality of analog devices, and a storage element storing an authentication value including a plurality of bits, a first bit of the plurality of bits based on measured electrical characteristics of a first subset of the analog devices, and a second bit of the plurality of bits based on measured electrical characteristics of a second subset of the analog devices, the second subset different from the first subset.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 15/029,555, filedApr. 14, 2016, which is a national stage application under 35 U.S.C.§371 of PCT/US2013/065038, filed Oct. 15, 2013, which are both herebyincorporated by reference in their entirety.

BACKGROUND

Fluid ejection devices such as print cartridges are used in, forexample, printers or other types of fluid dispensing systems to causefluid to be ejected on to a print or other type of medium to print animage. Verifying the authenticity of the fluid ejection device isadvisable.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 illustrates an implementation of a fluid ejection device inaccordance with various examples;

FIG. 2 illustrates a portion of a print head die in accordance withvarious examples;

FIG. 3 illustrates multiple drop generators disposed around a fluid feedslot in accordance with various examples;

FIG. 4 is a schematic representation of a fluid ejection device inaccordance with various examples;

FIG. 5 is a method for generating an authentication value for a fluidejection device in accordance with various examples; and

FIG. 6 is a method further elaborating on how the authentication valueis generated in accordance with various examples.

DETAILED DESCRIPTION

Reference is made herein to a “fluid ejection device.” Such a device maybe used in various applications such as in cartridges and printers. Thefluid to be ejected by the device may comprise printer ink, toner, clearliquid, or other types of fluid such as fluids for forensic orpharmaceutical applications. In some examples, a fluid ejection devicemay include a print head die (in some examples referred to as a printhead) and may also include a fluid reservoir. In some examples, the dieis the result of semiconductor wafer processing and includes at leastone semiconductor or electric component. In further examples, the dieincludes SU8 to facilitate fabrication of at least one component on thedie.

The illustrative fluid ejection device described herein includes astorage element for storing an authentication value usable to verify theauthenticity of the fluid ejection device. The authentication valuestored on the fluid ejection device is generated based on various analogdevices that are part of the fluid ejection device. In the examplesdisclosed below, the analog devices are firing resistors, but can beother than the resistors in other examples. In such examples, theauthentication value is generated based on the resistance of various ofthe firing resistors.

FIG. 1 shows a fluid ejection device 22 in accordance with one example.The fluid ejection device 22 includes a print head die 40 that ejectsdrops of fluid through a nozzle array 34 towards a print medium. Thenozzle array 34 includes a plurality of individual nozzles. The fluid isprovided to nozzle array 34 from a fluid reservoir. In someimplementations, the ink reservoir is integrated into the fluid ejectiondevice 22, while in other implementations, the ink reservoir is separatefrom the fluid ejection device, but connected to the fluid ejectiondevice through a fluidic connection such as a supply tube.

Nozzle array 34 may be arranged in the fluid ejection device 22 suchthat properly sequenced ejection of fluid from nozzle array 34 causescharacters, symbols, and/or graphics or images to be printed on to aprint medium as the fluid ejection device 22 and print medium are movedrelative to each other. The fluid ejection device 22 may be used as aconsumable, and thus a replaceable, component of a printer or otherfluid dispensing system.

The fluid ejection device 22 includes analog devices AD¹-A^(n+1). Insome examples, as described below, each analog device AD¹-A^(n+1)comprises a resistor such as a print head die firing resistor. In someexamples the firing resistor includes a thermal resistor. In otherexamples the analog device includes a piezo resistor. The analog devicesAD¹-A^(n+1) cause drops of fluid to be ejected on to a print medium. Theprint head die 40 also includes a storage element 70 which stores anauthentication value 72. The authentication value 72 is generated basedon comparisons AD¹/AD^(n), AD²/AD^(n+1) of at least some of the analogdevices AD¹-AD^(n+1). In some examples, each comparison AD¹/AD^(n),AD²/AD^(n+1), etc. is based on a difference between the measuredelectrical characteristics of a corresponding pair of analog devices AD¹and AD², AD^(n) and AD^(n+1), etc. For example, between two analogdevices, AD¹ and AD², a logic “1” may indicate that the electricalcharacteristic of AD¹ is greater than the electrical characteristic ofAD², while a logic “0” may indicate that the electrical characteristicfor AD¹ is less than the electrical characteristic for AD². In someexamples the measured electrical characteristics include a resistance ofa firing resistor.

The fluid ejection device 22 also includes an electrical connection 71through which the authentication value 72 can be provided to and storedin the storage element 70, and subsequently read from the storageelement 70 for purposes of, for example, authenticating the fluidejection device 22. The generation and use of the authentication valueis further explained below.

FIG. 2 is a diagram illustrating a portion of print head die 40 inaccordance with one example. The die may be part of a print head. Theprint head die 40 may include an array of fluid ejecting elements 42.Fluid ejecting elements 42 may be formed on a substrate 44, 48, 50,which has a fluid feed slot 46 formed therein. As such, fluid feed slot46 provides a supply of a fluid to fluid ejecting elements 42. Fluidfeed slot 46 is one example of a fluid feed source. Other examples offluid feed sources include corresponding individual fluid feed holesfeeding corresponding vaporization chambers and multiple shorter fluidfeed trenches that each feed corresponding groups of fluid ejectingelements. A thin-film structure 48 includes a fluid feed channel 54formed therein which communicates with fluid feed slot 46 formed insubstrate 44. An orifice layer 50 has a front face 50 a and a nozzleopening 34 a formed in front face 50 a. Nozzle opening 34 a is part ofnozzle array 34. Orifice layer 50 also includes a vaporization chamber56 formed therein which communicates with nozzle opening 34 a and fluidfeed channel 54 of thin-film structure 48. A firing resistor 52 a ispositioned within vaporization chamber 56 and leads 58 electricallycouple firing resistor 52 a to circuitry to control the application ofelectrical current through selected firing resistors. A drop generator60 may include firing resistor 52 a, vaporization chamber 56 and nozzleopening 34 a.

During printing, fluid flows from fluid feed slot 46 to vaporizationchamber 56 via fluid feed channel 54. Nozzle opening 34 a may beoperatively associated with firing resistor 52 a such that, uponenergizing of firing resistor 52 a, droplets of fluid withinvaporization chamber 56 are ejected through nozzle opening 34 a (e.g.,substantially normal to the plane of firing resistor 52 a) and toward aprint medium.

FIG. 3 is a diagram illustrating drop generators 60 located along fluidfeed slot 46 in one example of print head die 40. Fluid feed slot 46includes opposing fluid feed slot sides 46 a and 46 b. Drop generators60 are disposed along each of the opposing ink feed slot sides 46 a and46 b. A total of n drop generators 60 are located along fluid feed slot46, with m drop generators 60 located along fluid feed slot side 46 a,and n-m drop generators 60 located along fluid feed slot side 46 b. Inone example, n is 704, but any suitable number of drop generators 60 maybe disposed along fluid feed slot 46.

Fluid feed slot 46 provides fluid to each of the n drop generators 60disposed along fluid feed slot 46. Each of the n drop generators 60includes a firing resistor 52 a, a vaporization chamber 56 and a nozzleopening 34 a. Each of the n vaporization chambers 56 may be fluidicallycoupled to fluid feed slot 46 through at least one fluid feed channel54. The firing resistors 52 a of drop generators 60 are energized in acontrolled sequence to eject fluid from vaporization chambers 56 andthrough nozzle openings 34 a to print an image on a print medium.

FIG. 4 provides an example of a schematic representation of the fluidejection device 22. For example, the fluid ejection device 22 includesor is defined by a print head die 40. The fluid ejection device 22includes a plurality of analog devices such as firing resistors 52 a.The fluid ejection device 22 may also include a storage element 70 andan analog-to-digital converter (ADC) 80. The storage element comprisesany suitable type of non-transitory, non-volatile storage device. Asshown, the storage element 70 may be used to store an authenticationvalue 72 and a measurement sequence key 74. In some examples theresistors 52 a, the storage element 70 and the ADC 80 are integralcomponents of the print head die 40.

The authentication value 72 stored on the fluid ejection device 22 maybe calculated during manufacturing and assembly of the fluid ejectiondevice 22 based on at least some of the firing resistors 52 a. While thefiring resistors 52 a nominally may have the same resistance, inpractice due to manufacturing tolerances, the resistances of the firingresistors 52 a are not all identical. A resistance measurement devicethat has sufficient precision will be able to discern the resistivedifferences between the various firing resistors 52 a. The variabilityof the resistances is used as a “fingerprint” to generate a uniqueauthentication value for each fluid ejection device 22. Theauthentication value is stored in the storage element 70 of the fluidejection device by a host device (e.g., during manufacturing) and maysubsequently be used by a printer in which the fluid ejection device 22is installed to verify the authenticity of the fluid ejection device.For example, the printer may replicate the measurement of the variousfiring resistors to generate a second authentication value, compare thenewly generated second authentication value to the authentication value72 previously stored in the storage element 70 of the fluid ejectiondevice 22. If the two authentication values match, the fluid ejectiondevice 22 is deemed to be authentic; otherwise, the fluid ejectiondevice 22 is deemed not to be authentic.

In some implementations, the authentication value 72 is based on acomparison of resistances of pairs of firing resistors 52 a. Forexample, between two resistors, R1 and R2, a logic “1” may indicate thatthe resistance for R1 is greater than the resistance for R2, while alogic “0” may indicate that the resistance for R1 is less than theresistance for R2. Each bit of the authentication value thus mayrepresent the comparison of the measured resistances of a specific pairof firing resistors 52 a. If the authentication value is, for example, a16-bit value, then the comparison of 16 pairs of firing resistors 52 aare encoded in the authentication value. The authentication value 72 mayalso be encrypted.

The ADC 80 may be coupled between the electrical connection 71 (FIG. 1)and the analog devices 52 to facilitate measuring the electricalcharacteristics of the analog devices. In some examples, the ADC 80converts the electrical characteristics to a digital form to be storedon the storage element 70 in the form of the authentication value, forexample at the manufacturing stage. In further examples the ADC 80converts the electrical characteristics to a digital form to be read bya fluid dispensing system into which the fluid ejection device 22 isinstalled, and compared by the fluid dispensing system to theauthentication value 72 already stored on the storage element during anauthentication process. In some examples, the ADC 80 is an integralcomponent of the die 40 so that it can be used by a connected hostdevice (e.g., equipment at the manufacturing stage to initially sore theauthentication value 72 into the fluid ejection device 22 or a fluiddispensing system for authentication of the fluid ejection device) formeasuring the electrical characteristics.

Further still, the authentication value 72 initially may be formed as atristate value with each state indicating a result of a comparison ofthe electrical characteristics of a pair of firing resistors. One statemay indicate that a first firing resistor is greater than a secondfiring resistor, while a second state may indicate the first firingresistor is less than the second firing resistor. A third state mayindicate that the two firing resistors are approximately equal (e.g.,within a predetermined range of each other). These tristate values thenmay be converted to a sequence of binary bits (e.g., a larger binarynumber) to represent the authentication value 72 stored on the fluidejection device 22. The conversion of the tristate values to a binarynumber is a form of encryption, and the binary number may be furtherencrypted as desired.

Referring still to FIG. 4, the measurement sequence key 74 indicateswhich firing resistors 52 a were measured for the computation of theauthentication value 72 stored on the fluid ejection device 22. Themeasurement sequence key 74 may be used by a fluid dispensing systeminto which the fluid ejection device 22 is installed to determine whichfiring resistors were used to generate the authentication value 72 tothereby permit the dispensing system to recreate the same process forcomputing its own authentication value for authentication of the fluidejection device 22. The measurement sequence key may be any of multipledifferent values, each value specifying a specific set of firingresistors to be used in the comparison. The manufacturing equipment thatinitially generates the authentication value 72 and the fluid dispensingsystem that receives and authenticates the fluid ejection device 22 arepreprogrammed to determine based on the measurement sequence key 74which specific set of firing resistors are used in the firing resistorresistance comparisons to generate the authentication value.

FIG. 5 illustrates a method for generating the authentication value 72.FIG. 5 (and FIG. 6) refer to “analog devices.” In some implementationsanalog devices are firing resistors. At 100, the method includesmeasuring the electrical characteristics of a plurality of analogdevices (e.g., resistances of firing resistors). The measured electricalcharacteristics may be converted to digital values by the ADC 80. At102, the method further includes computing an authentication value basedon the measured electrical characteristics. The authentication value maybe encrypted. At 104, the method includes storing the generatedauthentication value on the fluid ejection device 22 (e.g., in thestorage element 70). The measurement sequence key 74 may be generatedand stored in storage element 70 to indicate which analog devices wereused to form the authentication value. At a later stage the fluidejection device 22 may be connected to, or otherwise installed in, afluid dispensing system and the electrical characteristics may bemeasured again, for example again through the ADC 80, and compared tothe (decrypted) authentication value to authenticate the fluid ejectiondevice 22.

FIG. 6 illustrates an implementation of operation 102 from FIG. 5. At110, electrical characteristics of multiple pairs of analog devices(e.g., resistances of firing resistors) are compared and at 112, theauthentication value is generated based on the results of thecomparisons of the measured electrical characteristics.

It will be appreciated that numerous variations and/or modifications maybe made to the above-described examples, without departing from thebroad general scope of the present disclosure. The present examples are,therefore, to be considered in all respects as illustrative and notrestrictive.

What is claimed is:
 1. A fluid ejection device, comprising: a pluralityof analog devices; and a storage element storing an authentication valueincluding a plurality of bits, a first bit of the plurality of bitsbased on measured electrical characteristics of a first subset of theanalog devices, and a second bit of the plurality of bits based onmeasured electrical characteristics of a second subset of the analogdevices, the second subset different from the first subset.
 2. The fluidejection device of claim 1, wherein the electrical characteristics of atleast some of the analog devices are measurable by a fluid ejectionsystem, and wherein the authentication value is usable by the fluidejection system to verify an authenticity of the fluid ejection devicebased on measured values of the at least some of the analog devices. 3.The fluid ejection device of claim 1, further comprising an electricalconnection to connect to a host device, the electrical connection beingconnected to the storage element to communicate the authentication valueto the host device, and being connected to the analog devices tofacilitate measuring of the electrical characteristics of at least someof the analog devices by the host device.
 4. The fluid ejection deviceof claim 3, further comprising an analog-to-digital converter coupledbetween the electrical connection and the analog devices to facilitatemeasuring the electrical characteristics of the at least some of theanalog devices.
 5. The fluid ejection device of claim 1, wherein theauthentication value is generated based on comparisons of the measuredelectrical characteristics of respective subsets of the at least some ofthe analog devices.
 6. The fluid ejection device of claim 1, wherein theauthentication value stored in the storage element is encrypted.
 7. Thefluid ejection device of claim 1, wherein the authentication valuecomprises an encrypted version of a comparison value, the comparisonvalue includes a plurality of bits, each bit to indicate a result of acomparison of the measured electrical characteristics of a respectivesubset of analog devices.
 8. The fluid ejection device of claim 1,wherein the storage element further stores a measurement sequence keythat indicates which analog devices were measured for a computation ofthe authentication value.
 9. The fluid ejection device of claim 1,wherein the analog devices comprise resistors, and the measuredelectrical characteristics include resistances of the resistors.
 10. Thefluid ejection device of claim 1, further comprising a connector tocommunicate the authentication value to a fluid dispensing system aspart of an authentication process performed by the fluid dispensingsystem to authenticate the fluid ejection device based on theauthentication value.
 11. A die comprising: a plurality of nozzles and aplurality of corresponding firing resistors; and a storage elementstoring an authentication value including a plurality of bits, a firstbit of the plurality of bits based on measured electricalcharacteristics of a first subset of the firing resistors, and a secondbit of the plurality of bits based on measured electricalcharacteristics of a second subset of the firing resistors, the secondsubset different from the first subset.
 12. The die of claim 11, furthercomprising an analog-to-digital converter to convert measured resistorvalues to digital values to facilitate measurement by a host device. 13.The die of claim 11, further comprising a connector to communicate theauthentication value to a fluid dispensing system as part ofauthenticating the die by the fluid dispensing system.
 14. The die ofclaim 11, wherein the storage element further stores a measurementsequence key that indicates which firing resistors were measured for acomputation of the authentication value.
 15. A die comprising: aplurality of analog devices; and a storage element storing anauthentication value including a plurality of bits, a first bit of theplurality of bits based on measured electrical characteristics of afirst subset of the analog devices, and a second bit of the plurality ofbits based on measured electrical characteristics of a second subset ofthe analog devices, the second subset different from the first subset.16. The die of claim 15, wherein the authentication value is encrypted.17. The die of claim 16, wherein encryption to provide theauthentication value includes a conversion from a tristate number to abase-2 number.